Nystagmus

Nystagmus

Definition

Nystagmus is a condition in which there is involuntary and rhythmic movement or oscillation of the eye. It is often caused by an underlying ocular or neurological disorder.

Description

The eye movements associated with nystagmus are varied. They can be either pendular, in which the oscillations are equal in all directions and or jerk, in which the movements may be faster in one direction than another. The frequency of the oscillation or movement and the amplitude of the oscillation also vary. The movements themselves may be vertical, horizontal, circular, or oblique in direction. Nystagmus can be sensory and develop as a result of poor vision, or it can be motor and develop as a result of a neurological problem.

Nystagmus may be congenital, or it may be acquired. Congenital, or infantile, nystagmus appears within the first few months of life. Congenital nystagmus is usually binocular and affects both eyes, is horizontal in direction, and does not occur while the child is sleeping. It decreases when the child's eyes converge or move inward. Most of these cases of nystagmus develop because of poor vision and do not have an underlying neurological cause.

Children with congenital nystagmus usually have a point in their eye movement in which the intensity of the nystagmus is decreased. This is called the null point, and the child may adopt a head tilt or rotation to help maintain his or her eyes at this position. This point is usually not in straight ahead or in a primary gaze position. Children with nystagmus who have their the null point located at a position in which the eyes are positioned inward may develop an esotropia, a form of strabismus or eye turn.

One variant of congenital nystagmus is spasmus nutans, which appears as a triad with accompanying head nodding and torticollis (head turn or tilt), and is seen between four months and three-and-a-half years of age and usually resolves without treatment within one to two years of onset. Rarely does it persist past age five. Usually spasmus nutans appears bilaterally, and the nystagmus is in a horizontal direction. When the nystagmus of spasmus nutans is vertical or rotary, the child does not have a head tilt.

There are various types of nystagmus. Downbeat nystagmus is characterized by a nystagmus that is more pronounced when the child looks down, especially when looking to the side, or in lateral gaze. An accentuated oscillation when looking up is seen in upbeat nystagmus. Seesaw nystagmus is an unusual type of in which one eye moves in and down and the other out and up. A periodic alternating nystagmus (PAN) is observed in primary gaze when the patient is looking straight ahead and is characterized by eye movements that continuously change direction and speed. Peripheral vestibular nystagmus may be accompanied by vertigo, nausea , and tinnitus, or ringing in the ears. This type of nystagmus is not always apparent but can be seen by a doctor when he or she looks in the back of the eye with a direct ophthalmoscope.

Latent nystagmus appears only when one eye is covered. This is a congenital nystagmus caused by an ocular motor disturbance rather than visual deprivation. It is often accompanied by strabismus or an eye turn. A child with latent nystagmus will not see well when one eye is covered.

Gaze evoked nystagmus occurs only when one is looking to the side in extreme lateral gaze. This type of nystagmus can be caused by ethanol and recreational drug use, but is seen in myasthenia gravis and thyroid disease as well.

Some types of nystagmus are normal. If one looks at an object in extreme gaze for a long period of time, endpoint nystagmus may be noted. Optokinetic nystagmus (OKN) is a nystagmus that can be elicited involuntarily when a rapidly moving striped object is passed in front of an individual's eyes.

Transmission

Congenital nystagmus may be transmitted genetically, either as an autosomal recessive or dominant, or as an X-linked recessive trait. It can also be associated with other conditions that are genetically transmitted. For example, Leber's amaurosis is an autosomal dominant trait and albinism is X-linked.

Demographics

Congenital nystagmus occurs twice as frequently in males than in females. The prevalence of nystagmus in the pediatric population is .015 percent. Eighty percent of nystagmus is congenital, and the remaining 20 percent is acquired.

Causes and symptoms

The eyes of an individual with nystagmus cannot remain still and oscillate in some position of gaze. Those
with nystagmus usually have decreased vision and poor depth perception, although those born with nystagmus, may not realize that their vision is poor. Those with acquired nystagmus may experience double vision or oscillopsia, or that objects in their visual space appear to move. An acquired nystagmus may be accompanied by other symptoms such dizziness , difficulty with balance, hearing loss, poor coordination, and numbness . If an individual with nystagmus experiences oscillopsia, then the nystagmus is acquired.

The primary cause of congenital nystagmus is visual deprivation, and the causes of visual deprivation in an infant include cataracts, oculoalbinism, glaucoma, retinal detachments, Leber's amaurosis, developmental abnormalities of the optic nerve such as a coloboma, and achromatopsia, a condition in which the infant cannot see color.

Acquired nystagmus can be caused by demyelination of nerve fibers, such as occurs in multiple sclerosis, lesions or tumors of the vestibular or visual pathways, strokes of the central nervous system, and drug use, both recreational as well as a side effect of prescribed drugs, such as those used to treat seizures and depression. Other causes of acquired nystagmus are Arnold-Chiari malformations, vitamin deficiencies, syphilis, Wernicke's encephalopathy, Behcet's syndrome, and Meniere's disease.

When to call the doctor

Since nystagmus can be caused by tumors, stroke , and trauma or neurological disorder, any type of nystagmus must be evaluated by a qualified practitioner. The nystagmus can be a sign of a serious problem. For example, a type of tumor called chiasmal glioma has signs and symptoms similar to spasmus nutans.

Diagnosis

Diagnosis of nystagmus is made primarily by patient history as reported by a parent, the age of onset, and observation of any accompanying signs such as a head turn, tilt or tremor, or oscillopsia. If possible, the infant or child's best visual acuity is determined. If the onset is acute, then usually the nystagmus is acquired.

The type of nystagmus can accurately be determined by eye movement recordings, which map direction, frequency, null point, and amplitude of the nystagmus. For the infant with congenital nystagmus, evoked response potential (EVR) and electroretinogram (ERG) give the doctor objective information about visual potential, and magnetic resonance imaging (MRI) can determine if and where a lesion is located. For the infant or young child, some of these tests may be done under anesthesia.

Treatment

The treatment for nystagmus, once the etiology is determined and treated, includes optical devices such as contact lenses and glasses, medication, and surgery.

For individuals with nystagmus correction of refractive error with glasses or contact lenses is the first step in treating the condition. For 85 percent of children with nystagmus, a spectacle prescription improves vision significantly. For those with congenital nystagmus, prism may be put in glasses to help position the eye at its null point or to help the eyes converge. For some people contact lenses are prescribed. Contact lenses slow down eye movements, and because the optical center of the prescription is always centered on the eye with the contact lens, vision improves. Low vision aids such as telescopes assist those whose vision cannot be fully corrected with spectacles and contact lenses alone. Tinting of the glasses or sunglasses may decrease the nystagmus of individuals with albinism. For the patient with oscillopsia, grinding prism into the spectacles may move the visual field to a point of decreased oscillopsia.

Congenital nystagmus, when due to a visual deprivation, is rarely improved by surgery. But when a head tilt or head turn accompanies nystagmus, surgery to correct a muscle imbalance may improve nystagmus and visual acuity. Surgery on the extraocular muscles of the eye may be helpful when the child's null point is in not in primary gaze but located at least 30 degrees from straight-ahead vision. When a tumor or stroke has caused an acquired nystagmus, then neurosurgery, if indicated for the underlying cause, may lead to resolution of the nystagmus. When surgery is considered, the risks of anesthesia must also be considered.

If oscillopsia is a co-existing symptom, then drugs can be given to reduce the ocular oscillations. Vestibular nystagmus can be treated by diazepam or scopolamine. Drugs called GABA agonists, such as baclofen and carbamazepine, are useful in treatment of seesaw nystagmus and PAN, if the nystagmus is acquired and not congenital. Baclofen cannot be given to children.

Botox (Botulinum toxin) injections can temporarily control the eye movements, but because of side effects such as double vision and ptosis or drooping of the eyelid, and because it is not a permanent solution, Botox is not used often.

If the nystagmus is due to drug toxicity, then reducing or discontinuing the drug eventually resolves the problem.

Alternative treatment

Acupuncture and biofeedback and vision therapy have been successful for some patients.

Prognosis

Congenital nystagmus is usually a benign condition. It is not curable, but its symptoms can be diminished with spectacles or contact lenses. The best corrected vision for most individuals with congenital nystagmus is between 20/40 and 20/70, but correction to 20/20 is possible for some. Nystagmus associated with spasmus nutans resolves spontaneously before the child reaches school age.

The prognosis for an acquired nystagmus depends on its cause. If the condition is due to a side effect of a drug, then decreasing or changing the treatment drug eventually resolves the nystagmus.

Prevention

In general nystagmus cannot be prevented. Since the cause of acquired nystagmus can be due to a co-existing neurological condition, prompt attention to other neurological signs that may accompany nystagmus, such as dizziness, may prevent or decrease the severity of nystagmus itself. Careful monitor of dosage of those drugs with nystagmus as a side effect may prevent the condition.

Parental concerns

Because nystagmus can be associated with many medical problems, the child with this condition must undergo a complete ocular and neurological evaluation.

Children with nystagmus are not aware that they may have a visual deficiency and as they get older must be helped with the restrictions that nystagmus places on them. For instance, driving may be restricted or not permitted. Certain occupations for which good visual correction is a requirement may be not feasible. Every effort must be made to integrate the child with nystagmus into a normal school setting in order to prepare the child for adult life, even if cosmetic concerns may instinctively lead the parent to want to protect the child.

Support for families of those with nystagmus can be found through the American Nystagmus Network.

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Nystagmus

Gale Encyclopedia of Medicine, 3rd ed.
COPYRIGHT 2006 Thomson Gale

Nystagmus

Definition

Rhythmic, oscillating motions of the eyes are called nystagmus. The to-and-fro motion is generally involuntary. Vertical nystagmus occurs much less frequently than horizontal nystagmus and is often, but not necessarily, a sign of serious brain damage. Nystagmus can be a normal physiological response or a result of a pathologic problem.

Description

The eyes play a critical role in maintaining balance. They are directly connected to other organs of equilibrium, most important of which is the inner ear. Paired structures called the semicircular canals deep in the skull behind the ears sense motion and relay that information to balance control centers in the brain. The eyes send visual information to the same centers. A third set of sensors consists of nerve endings all over the body, particularly in joints, that detect position. All this information is integrated to allow the body to navigate in space and gravity.

It is possible to fool this system or to overload it with information so that it malfunctions. A spinning ride at the amusement park is a good way to overload it with information. The system has adapted to the spinning, expects it to go on forever, and carries that momentum for some time after it is over. Nystagmus is the lingering adjustment of the eyes to tracking the world as it revolves around them.

Nystagmus can be classified depending upon the type of motion of the eyes. In pendular nystagmus the speed of motion of the eyes is the same in both directions. In jerk nystagmus there is a slow and fast phase. The eyes move slowly in one direction and then seem to jerk back in the other direction.

Nystagmus can be present at birth (congenital) or acquired later on in life. A certain type of acquired nystagmus, called spasmus nutans, includes a head tilt and head bobbing and generally occurs between four to 12 months of age. It may last a few months to a few years, but generally goes away by itself.

Railway nystagmus is a physiological type of nystagmus. It happens when someone is on a moving train (thus the term railway) and is watching a stationary object which appears to be going by. The eyes slowly follow the object and then quickly jerk back to start over. Railway nystagmus (also called optokinetic nystagmus) is a type of jerk nystagmus. This phenomenon can be used to check vision in infants. Nystagmus can also be induced by fooling the semicircular canals. Caloric stimulation refers to a medical method of testing their connections to the brain, and therefore to the eyes. Cold or warm water flushed into the ear canal will generate motion signals from the inner ear. The eyes will respond to this signal with nystagmus if the pathways are intact.

Causes and symptoms

There are many causes of nystagmus. Nystagmus may be present at birth. It may be a result of the lack of development of normal binocular fixation early on in life. This can occur if there is a cataract at birth or a problem is some other part of the visual system. Some other conditions that nystagmus may be associated with include:

Albinism. This condition is caused by a decrease in pigmentation and may affect the eyes.

Disorders of the eyes. This may include optic atrophy, color blindness, very high nearsightedness (myopia ) or severe astigmatism, or opacities in the structures of the eyes.

Acute labyrinthitis. This is an inflammation in the inner ear. The patient may have dizziness (vertigo), nausea and vomiting, and nystagmus.

Brain lesions. Disease in many parts of the brain can result in nystagmus.

Alcohol and drugs. Alcohol and some medications (e.g., anti-epilepsy medications) can induce or exaggerate nystagmus.

Multiple sclerosis. A disease of the central nervous system.

Diagnosis

Nystagmus is a sign, not a disease. If abnormal, it indicates a problem in one of the systems controlling it. An ophthalmologist and/or neuro-ophthalmologist should be consulted.

Treatment

There is one kind of nystagmus that seems to occur harmlessly by itself. The condition, benign positional vertigo, produces vertigo and nystagmus when the head is moved in certain directions. It can arise spontaneously or after a concussion. Motion sickness medicines sometimes help. But the reaction will dissipate if continuously evoked. Each morning a patient is asked to produce the symptom by moving his or her head around until it no longer happens. This prevents it from returning for several hours or the entire day.

Prisms, contact lenses, eyeglasses, or eye muscle surgery are some possible treatments. These therapies may reduce the nystagmus but may not alleviate it. Again, because nystagmus may be a symptom, it is important to determine the cause.

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nystagmus

nystagmus is a disorder of eye movements, when they show involuntary, rhythmic oscillations. The name is from the Greek, depicting the slow nodding of drowsiness accompanied by irregular, quick raising of the chin. Clinically, most nystagmus is horizontal in direction, but vertical and torsional forms can occur. It usually presents a diagnostic challenge and special tests are used to induce nystagmus and elucidate the neurological cause. Two major groups are recognized: jerk nystagmus, with oscillations that are faster in one direction than in the other, creating a jerky rhythm; and pendular nystagmus, with oscillations that are roughly equal in speed to either side.

Jerk nystagmus is named according to the direction of the fast phase, although the slower, return movement that regains and holds ocular fixation is more important functionally. Such movements are easily seen in someone looking out of a moving train who is trying to count the railway sleepers in the adjacent track. The fast phase is in the direction of travel of the train. Such opto-kinetic nystagmus (OKN) can be demonstrated by rotating a cylindrical drum painted with black vertical stripes in front of the subject: the eyes will move in the direction of drum rotation, followed by a quick return to fixate on the next moving stripe. The urge to follow these movements is so powerful that OKN can even be used to prove vision in someone claiming to be blind.

Jerk nystagmus can also result from stimulation of the semicircular canals of the vestibular system. There are two groups of three canals that lie in three planes at right angles to each other in either side of the skull. Stimulation of these canals by head movement causes ocular movements that maintain the eyes' positions in space and so stabilize the field of view. If the head movement causes the eyes to reach the limit of comfortable sideward gaze the eyes make a fast, compensatory movement to the central position. Careful testing with OKN and vestibular-induced nystagmus can be used to pinpoint the site of neurological defects in some disease conditions.

Pendular nystagmus is found with loss of central, detail vision, such as occurs with bilateral macular lesions present from birth in albinism, aniridia (absence of the iris), or total colour blindness. There are rapid, pendular eye movements in miners' nystagmus' and the condition was attributed to defective illumination in mines. This occupational nystagmus has now been effectively eliminated by adequate lighting underground.

Congenital nystagmus can occur without other defects. The nystagmus appears pendular in straight-ahead gaze and becomes jerky on side gaze. Although visual acuity in the distance is always reduced, and usually to levels below the legal requirements for driving, reading can be surprisingly good, provided that the patient is allowed to hold the book in the preferred position. This may be closer than normal and with the head turned to one side. Parents of a child with congenital nystagmus may gain some comfort from the descriptive term ‘dancing eyes’ and from the knowledge that, with understanding teachers, education at a normal school followed by university is achievable.

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nystagmus

nystagmus (nis-tag-mŭs) n. rapid involuntary movements of the eyes that may be from side to side, up and down, or rotatory. Nystagmus may be congenital and associated with poor sight; it also occurs in disorders of the part of the brain responsible for eye movements and in disorders of the organ of balance in the ear.

Cite this article Pick a style below, and copy the text for your bibliography.

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